Modern residential buildings are often equipped with a central air circulation and delivery system, which utilizes an air blower fan to force air into individual rooms through an air delivery duct system in the buildings. When the circulated air is heated or cooled or otherwise conditioned, circulation of the air inside a building also provides heating or cooling of ambient temperature or otherwise conditioning of air in the building or individual rooms thereof. It is desirable that each room is heated, cooled or otherwise conditioned according to user selectable criteria for the comforts of the room's occupants.
Such a centralized air circulation and delivery system, however, does not always provide satisfactory results. For example, in a residential building, the air blower may be installed in a basement while a bedroom may be two or three floors up. An air blower fan may not be sufficiently powerful to deliver the desired volume of air to such a bedroom, thereby may not be able to heat or cool the room to the desired temperature. In addition, distances from different rooms to the air blower fan are generally different. The duct system may not be always designed to compensate for the different lengths of duct paths to reach individual rooms, with the result of uneven distribution and delivery of air in individual rooms in a building. To compensate, people tend to set temperature a little higher (in the winter) or a little lower (in the summer) for the entire building so that they may feel comfortable in the room or rooms with insufficient air delivery. This generally wastes energy.
Traditionally, damper balancing has been used to balance air delivery. Air is discharged into each room through a vent or vents. A damper is provided near each vent for controlling the air supply to the vent. Thus, a damper may be used to partially close off or otherwise reduce or restrict airflow to rooms with stronger air delivery while leaving the dampers fully open in a duct or ducts leading to other rooms that require more air delivery, thus achieving a more balanced delivery of air to all rooms. Each vent may be further equipped with an adjustable register, which is provided with louvers. Adjusting the louvers can further control volume of airflow through the register. This solution does not provide a satisfactory solution. Dampers are generally located some distance away from vents or may be hidden behind floor or wall coverings and therefore difficult to reach. Restricting or reducing air flow at some vents generally reduces the efficiency of the entire air delivery system. Air flow at other vents is not necessarily increased, or increased proportionally as a result of the reduction at the closed off or blocked vents. The efficiency of the air circulation and delivery system tends to be reduced as a result. More importantly, restricting air flow in some rooms results in air not being sufficiently circulated in these rooms. Sometimes, this may also produce the undesirable result of whistling at vents that are almost entirely closed off.
There have been other solutions proposed based on a booster fan installed over a register. Typically, such a booster fan has a housing enclosing a fan inside. For example, U.S. Pat. No. 4,846,399 discloses a register booster fan for increasing the flow of air through a register. U.S. Pat. No. 5,489,283 discloses another register booster fan that includes a centrifugal fan for drawing air from the register and redirecting air horizontally outwardly through side vents of the booster fan. These booster fans rest on a register with its air inlet facing the register. The fan directs air upwardly and draws air from the register, thereby increasing the air flow through the register. However, this solution is not entirely satisfactory. Such a booster fan, resting above a register, may create an obstacle on the floor. Being positioned on top of a register, it may also alter a room's otherwise aesthetic appearance. In addition, such a booster fan requires good sealing between the booster fan and the register in order to maintain a negative air pressure at the register for drawing air from the register and for avoiding ambient air being drawn into the booster fan and re-circulated.
There have also been proposals of in-line air duct booster fans. A booster fan of this type is generally installed in an air duct for increasing the air flow along a duct. However, an air duct may be used for delivering air into several different rooms, not all of which require a booster. Increasing air flow in a duct may cause further imbalance of air delivery in individual rooms. There have also been booster fans proposed that are installed in a vent opening directly under a register. For example, U.S. Pat. No. 5,632,677 discloses a fan-equipped vent for installation in a vent opening under a register. The fan-equipped vent has a housing that fits inside a typical vent opening in a residential building and encloses one or several fans. As the fan-equipped vent has to fit within the available space of a typical vent opening, the size of a fan or fans used inside the housing is more restricted. This size limit tends to limit the ability of fans to move air. To compensate, more than one fan or increased fan speed is generally required. This tends to increase the noise level and may disturb the occupant's quiet enjoyment in a room. As more fans are used within a confined space, they may also obstruct air flow, which may partially defeat the purpose of installing such a booster fan.
There is therefore a need for an improved booster fan for use in a central air circulation and delivery system. It is an object of the present invention to mitigate or obviate at least one of the above mentioned disadvantages.